In 1982, my family took delivery of the very first IBM-PC in Israel. We actually went down to the warehouse and waited while our PC was delivered from the port. Somehow, I convinced my dad to get the fully-decked out version, with two floppy disks, 128 K memory, and both a dot-matrix printer (for fast drafts) and a Brother Letter-Quality Daisy Wheel printer, which sounds exactly like a machine gun when it is operating, only louder. I think we got almost every accessory available: PC-DOS 1.0, the $75 technical reference manual with a complete source code listing of the BIOS, Macro Assembler, and the stunning IBM Monochrome display with a full 80 columns and ... lower case letters! The whole thing cost about $10,000 including Israel's then-ridiculous import taxes. Extravagant!
Now, "everybody" knew that BASIC was a children's language that requires you to write spaghetti code and turns your brain into Camembert cheese. So we shelled out $600 for IBM Pascal, which came on three floppy diskettes. The compiler's first pass was on the first diskette, the second pass was on the second diskette, and the linker was on the third diskette. I wrote a simple "hello, world" program and compiled it. Total time elapsed: 8 minutes.
Hmm. That's a long time. I wrote a batch file to automate the process and shaved it down to 7 1/2 minutes. Better. But when I tried to write long programs like my stunning version of Othello which always beat me, I spent most of the time waiting for compiles. "Yep," a professional programmer told me, "we used to keep a sit-up board in the office and do sit-ups while we were doing compiles. After a few months of programming I had killer abs."
One day, a spiffy program called Compas Pascal appeared from Denmark, which Philippe Kahn bought and renamed Borland Turbo Pascal. Turbo Pascal was sort of shocking, since it basically did everything that IBM Pascal did, only it ran in about 33K of memory including the text editor. This was nothing short of astonishing. Even more astonishing was the fact that you could compile a small program in less than one second. It's as if a company you had never heard of introduced a clone of the Buick LeSabre which could go 1,000,000 MPH and drive around the world on so little gasoline than an ant could drink it without getting sick.
Suddenly, I became much more productive.
That's when I learned about the concept of the REP loop. REP stands for "Read, Eval, Print", and it describes what a lisp interpreter does for a living: it "reads" your input, evaluates it, and prints the result. An example of the REP loop is shown below: I type something, and the lisp interpreter reads it, evaluates it, and prints the result.
On a slightly larger scale, when you're writing code, you are in a macro-version of the REP loop called the Edit-Compile-Test loop. You edit your code, compile it, test it, and see how well it works.
A crucial observation here is that you have to run through the loop again and again to write a program, and so it follows that the faster the Edit-Compile-Test loop, the more productive you will be, down to a natural limit of instantaneous compiles. That's the formal, computer-science-y reason that computer programmers want really fast hardware and compiler developers will do anything they can to get super-fast Edit-Compile-Test loops. Visual Basic does it by parsing and lex-ing each line as you type it, so that the final compile can be super-quick. Visual C++ does it by providing incremental compiles, precompiled headers, and incremental linking.
But as soon as you start working on a larger team with multiple developers and testers, you encounter the same loop again, writ larger (it's fractal, dude!). A tester finds a bug in the code, and reports the bug. The programmer fixes the bug. How long does it take before the tester gets the fixed version of the code? In some development organizations, this Report-Fix-Retest loop can take a couple of weeks, which means the whole organization is running unproductively. To keep the whole development process running smoothly, you need to focus on getting the Report-Fix-Retest loop tightened.
One good way to do this is with daily builds. A daily build is an automatic, daily, complete build of the entire source tree.
Automatic - because you set up the code to be compiled at a fixed time every day, using cron jobs (on UNIX) or the scheduler service (on Windows).
Daily - or even more often. It's tempting to do continuous builds, but you probably can't, because of source control issues which I'll talk about in a minute.
Complete - chances are, your code has multiple versions. Multiple language versions, multiple operating systems, or a high-end/low-end version. The daily build needs to build all of them. And it needs to build every file from scratch, not relying on the compiler's possibly imperfect incremental rebuild capabilities.
Here are some of the many benefits of daily builds:
Here's how to do them. You need a daily build server, which will probably be the fastest computer you can get your hands on. Write a script which checks out a complete copy of the current source code from the repository (you are using source control, aren't you?) and then builds, from scratch, every version of the code that you ship. If you have an installer or setup program, build that too. Everything you ship to customers should be produced by the daily build process. Put each build in its own directory, coded by date. Run your script at a fixed time every day.
For Further Reading:
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